Recording/reproduction apparatus, recording/reproduction method, program, and recording power adjustment apparatus

ABSTRACT

A recording/reproduction apparatus, comprising a first recording section for recording test information onto a medium using at least one recording power, a reproduction section for reproducing at least one test signal indicating the test information from the medium, and a second recording section for recording information onto the medium using one of the at least one recording power. The reproduction section comprises a decoding section for performing maximum likelihood decoding of the at least one test signal and generating at least one binary signal indicating a result of the maximum likelihood decoding, a calculation section for calculating a reliability of the result of the maximum likelihood decoding based on the at least one test signal and the at least one binary signal, and an adjustment section for adjusting a recording power for recording the information onto the medium to the one recording power based on the reliability.

This is a divisional application of U.S. application Ser. No. 10/981,869filed on Nov. 5, 2004 which claims priority under 35 U.S.C. §119 (a) onPatent Application No. 2003-376855 filed in Japan on Nov. 6, 2003, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording/reproduction apparatus,recording/reproduction method, program, and recording power adjustmentapparatus capable of adjusting a recording power (e.g., a write power,an erase power, or a bottom power). More particularly, the presentinvention relates to a recording/reproduction apparatus,recording/reproduction method, program, and recording power adjustmentapparatus capable of adjusting a recording power7 based on a partialresponse maximum likelihood (PRML) technique which is a type ofreproduction technique.

2. Description of the Related Art

Phase change optical discs (CD-RW, DVD-RAM, DVD-RW, Blu-ray Disc, etc.)are known as rewritable optical discs. For phase change optical discs,multipulse laser light is used to perform overwrite recording. Laserlight has, for example, a write power Pw, an erase power Pe and a bottompower Pb.

FIG. 24 shows a multipulse having a write power Pw, an erase power Peand a bottom power Pb.

The write power Pw is used to change the state of a recording film froma crystal state to an amorphous state so as to form a mark. The erasepower Pe is used to change the state of the recording film from theamorphous state to the crystal state so as to erase (overwrite) an oldmark. The bottom power Pb corresponds to a power of a bottom portion ofa multipulse, and is used to prevent thermal diffusion due toirradiation of laser light during recording using a multipulse.

Conventionally, in recording/reproduction methods andrecording/reproduction apparatuses for recording digital informationonto a recording medium, a test signal is recorded onto a recordingmedium while changing the write power Pw, the erase power Pe and thebottom power Pb in various manners, and the recorded test signal isreproduced. A predetermined signal evaluation index is detected todetermine whether or not the recorded state of the signal is normal. Inorder to achieve the recorded state which allows an optimum or desiredstate of a predetermined signal evaluation index, the power of laserlight is controlled and determined. Examples of the predetermined signalevaluation index include jitter, asymmetry, an error rate (a bit errorrate (SER)), the degree of modulation, and the like (e.g., Japan PatentNo. 3259642 (particularly, FIG. 1)).

Alternatively, a method for controlling and determining the power oflaser light by referencing a signal evaluation index based on a PRMLexpected value error has been proposed. For example, Partial ResponseMaximum Likelihood (PRML) is a signal processing technique which can beexpected to improve reproduction performance when original digitalinformation is reproduced from a recording medium. PRML is a combinationof waveform equalization called PR and maximum likelihood decodingcalled ML.

Conventionally, the characteristics of a recording/reproductiontransmission path are evaluated based on jitter in a binary pulse and areproduced cloak. However, it has been difficult to evaluate andoptimize the characteristics of a reproduction transmission path basedon the PRML technique. This is because jitter is not correlated with theperformance (BER) of the PRML technique.

For example, Japanese Laid-Open Publication No. 2003-141823(particularly, page 79, expression (14); page 173, and FIG. 14)discloses a technique in which an expected value error correlated withthe HER of the PRML technique is used as an index instead of jitter.This index is used as an index to indicate the probability of occurrenceof error due to stress in a reproduction system, such as a focus offset,a tilt or the like. The index is also used in best focus search or thelike. In other words, the index is used to optimize a parameter whichdetermines whether or not a reproduced state is normal.

However, in a method and apparatus which determines an optimum recordingpower using asymmetry as an index, the optimum power may not be obtaineddue to insufficient precision in detection of asymmetry. In a method andapparatus which determines an optimum recording power with the PIMtechnique using jitter as an index, the optimum power may not becorrectly obtained, since a recording power minimizing jitter is notnecessarily equal to a recording power minimizing HER. In a method andapparatus which determines an optimum recording power with the PRMLtechnique using BER as an index, the optimum power may not be obtaineddue to insufficient precision in detection of the index. Theinsufficient precision of detection of the indexes is attributed to therequirement of a large quantity of recording area for measurement ofBER, the degradation of BER due to stain, dust or the like on a discrather than a recorded state, a change in BER (sensitivity) to arecording power due to the high error correction capability of the PRMLtechnique, or the like.

As described above, when a conventional method of setting a parameterfor a recording power in a manner which optimizes jitter, asymmetry orBER (e.g., Japan Patent No. 3259642) is applied to a system whichemploys the PRML technique, the probability of occurrence of error isnot necessarily minimized. In addition, a recording power is notnecessarily determined with good precision due to insufficient precisionof detection of an index for determining a recording power. Therefore, adegradation in performance occurs due to cross power (overwrite isperformed on a recorded area of a disc under different conditions),which is generated due to error in setting a recording power. Therefore,it may be difficult to obtain the stable compatibility of optical discdrive apparatuses and optical disc media to the same standard.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, arecording/reproduction apparatus is provided, which comprises a firstrecording section for recording at least one piece of test informationonto a medium using at least one recording power, a reproduction sectionfor reproducing at least one test signal indicating the at least onepiece of test information from the medium, and a second recordingsection for recording information onto the medium using one of the atleast one recording power. The reproduction section comprises a decodingsection for performing maximum likelihood decoding of the at least onetest signal and generating at least one binary signal indicating aresult of the maximum likelihood decoding, a calculation section forcalculating a reliability of the result of the maximum likelihooddecoding based on the at least one test signal and the at least onebinary signal, and an adjustment section for adjusting a recording powerfor recording the information onto the medium to the one recording powerbased on the reliability.

In one embodiment of this invention, the calculation section calculatesthe reliability based on a test signal of the at least one test signalcorresponding to an edge of a recorded mark formed on the medium and abinary signal of the at least one binary signal corresponding to theedge of the recorded mark.

In one embodiment of this invention, the calculation section calculatesthe reliability based on a plurality of test signals corresponding toedges of a plurality of recorded marks formed on the medium and aplurality of binary signals corresponding to the edges of the pluralityof recorded marks.

In one embodiment of this invention, the first recording section recordsa piece of test information onto the medium using a plurality ofrecording powers.

In one embodiment of this invention, the first recording section recordsa plurality of pieces of test information onto the medium using aplurality of recording powers.

In one embodiment of this invention, the first recording section recordsa piece of test information onto the medium using a single recordingpower.

In one embodiment of this invention, the first recording section recordsa plurality of pieces of test information onto the medium using a singlerecording power.

In one embodiment of this invention, the reproduction section reproducesat least one first signal indicating the information from the medium.The decoding section performs maximum likelihood decoding of the atleast one first signal and generates at least one first binary signalindicating a result of the maximum likelihood decoding. The calculationsection calculates a reliability of the result of the maximum likelihooddecoding based on the at least one first signal and the at least onefirst binary signal. The adjustment section adjusts a recording powerfor recording information onto the medium based on the reliability.

In one embodiment of this invention, the recording power to be adjustedincludes at least one of a write power, an erase power and a bottompower.

In one embodiment of this invention, the at least one test signalincludes a pattern having a shortest data cycle and a pattern having alongest data cycle in a recording modulation rule, and the probabilityof occurrence of a recorded mark is equal to the probability ofoccurrence of a space.

In one embodiment of this invention, the calculation section calculatesmodulation degree characteristics based on an amplitude of the at leastone test signal. The adjustment section adjusts a recording power forrecording the information onto the medium to the one recording powerbased on at least one of the reliability and the modulation degreecharacteristics.

In one embodiment of this invention, the adjustment section adjusts atleast one of an erase power and a bottom power based on the reliability.The adjustment section adjusts a write power based on the modulationdegree characteristics.

In one embodiment of this invention, a test signal for calculating thereliability includes the pattern having the shortest data cycle and thepattern having the longest data cycle, and the probability of occurrenceof the recorded mark is equal to the probability of occurrence of thespace. A test signal for calculating the modulation degreecharacteristics includes the pattern having the longest data cycle.

In one embodiment of this invention, the decoding section comprises anA/D conversion section for sampling the at least one test signal using atest clock synchronized with the at least one test signal, a digitalfilter for shaping a waveform of data output from the A/D conversionsection to predetermined PR equalization characteristics, and a maximumlikelihood decoding section for generating at least one binary signal,which is most probable, from output data of the digital filter. Thecalculation section comprises a differential metric detection sectionfor detecting a reliability value of a result of decoding by the maximumlikelihood decoding section based on a state transition sequenceestimated by the maximum likelihood decoding section and a result ofcalculation of an Euclid distance between the output data of the digitalfilter and a target value used in maximum likelihood decoding, and adetermination section for determining whether or not a recorded state isnormal based on an output of the differential metric detection section.The adjustment section comprises a laser power control section forcontrolling a laser power to output laser light having a predeterminedrecording power.

In one embodiment of this invention, the calculation section furthercomprises a modulation degree detection section for detecting themodulation degree characteristics based on an amplitude of the at leastone test signal. The determination section determines whether or not therecorded state is normal based on at least one of an output of thedifferential metric detection section and an output of the modulationdegree detection section.

In one embodiment of this invention, the decoding section performsmaximum likelihood decoding using a recording code having a minimumpolarity reversal interval of 2 and a state transition rule defined byan equalization system PR (C0, C1, C1, C0).

According to another aspect of the present invention, arecording/reproduction apparatus is provided, which comprises a firstrecording section for recording at least one piece of test informationonto a medium using at least one recording power, a reproduction sectionfor reproducing at least one test signal indicating the at least onepiece of test information from the medium, and a second recordingsection for recording information onto the medium using one of the atleast one recording power. The reproduction section comprises a decodingsection for performing maximum likelihood decoding of the at least onetest signal and generating at least one binary signal indicating aresult of the maximum likelihood decoding, a calculation section forcalculating a reliability of the result of the maximum likelihooddecoding based on a test signal of the at least one test signalcorresponding to an edge of a recorded mark formed on the medium and abinary signal of the at least one binary signal corresponding to theedge of the recorded mark, and an adjustment section for adjusting arecording power for recording the information onto the medium to the onerecording power based on the reliability.

According to another aspect of the present invention, arecording/reproduction method is provided, which comprises recording atleast one piece of test information onto a medium using at least onerecording power, reproducing at least one test signal indicating the atleast one piece of test information from the medium, and recordinginformation onto the medium using one of the at least one recordingpower. The reproducing step comprises performing maximum likelihooddecoding of the at least one test signal and generating at least onebinary signal indicating a result of the maximum likelihood decoding,calculating a reliability of the result of the maximum likelihooddecoding based on the at least one test signal and the at least onebinary signal, and adjusting a recording power for recording theinformation onto the medium to the one recording power based on thereliability.

According to another aspect of the present invention, arecording/reproduction method is provided, which comprises recording atleast one piece of test information onto a medium using at least onerecording power, reproducing at least one test signal indicating the atleast one piece of test information from the medium, and recordinginformation onto the medium using one of the at least one recordingpower. The reproducing step comprises performing maximum likelihooddecoding of the at least one test signal and generating at least onebinary signal indicating a result of the maximum likelihood decoding,calculating a reliability of the result of the maximum likelihooddecoding based on a test signal of the at least one test signalcorresponding to an edge of a recorded mark formed on the medium and abinary signal of the at least one binary signal corresponding to theedge of the recorded mark, and adjusting a recording power for recordingthe information onto the medium to the one recording power based on thereliability.

According to another aspect of the present invention, a program forcausing a computer to execute a recording power adjustment procedure isprovided. The recording power adjustment procedure comprises recordingat least one piece of test information onto a medium using at least onerecording power, reproducing at least one test signal indicating the atleast one piece of test information from the medium, and recordinginformation onto the medium using one of the at least one recordingpower. The reproducing step comprises performing maximum likelihooddecoding of the at least one test signal and generating at least onebinary signal indicating a result of the maximum likelihood decoding,calculating a reliability of the result of the maximum likelihooddecoding based on the at least one test signal and the at least onebinary signal, and adjusting a recording power for recording theinformation onto the medium to the one recording power based on thereliability.

According to another aspect of the present invention, a program forcausing a computer to execute a recording power adjustment procedure isprovided. The recording power adjustment procedure comprises recordingat least one piece of test information onto a medium using at least onerecording power, reproducing at least one test signal indicating the atleast one piece of test information from the medium, and recordinginformation onto the medium using one of the at least one recordingpower. The reproducing step comprises performing maximum likelihooddecoding of the at least one test signal and generating at least onebinary signal indicating a result of the maximum likelihood decoding,calculating a reliability of the result of the maximum likelihooddecoding based on a test signal of the at least one test signalcorresponding to an edge of a recorded mark formed on the medium and abinary signal of the at least one binary signal corresponding to theedge of the recorded mark, and adjusting a recording power for recordingthe information onto the medium to the one recording power based on thereliability.

According to another aspect of the present invention, a recording poweradjustment apparatus is provided, which comprises a decoding section forperforming maximum likelihood decoding of at least one test signal froma medium and generating at least one binary signal indicating a resultof the maximum likelihood decoding, a calculation section forcalculating a reliability of the result of the maximum likelihooddecoding based on the at least one test signal and the at least onebinary signal, and an adjustment section for adjusting a recording powerfor recording the information onto the medium to the one recording powerbased on the reliability.

According to another aspect of the present invention, a recording poweradjustment apparatus is provided, which comprises a decoding section forperforming maximum likelihood decoding of at least one test signal froma medium and generating at least one binary signal indicating a resultof the maximum likelihood decoding, a calculation section forcalculating a reliability of the result of the maximum likelihooddecoding based on a test signal of the at least one test signalcorresponding to an edge of a recorded mark formed on the medium and abinary signal of the at least one binary signal corresponding to theedge of the recorded mark, and an adjustment section for adjusting arecording power for recording the information onto the medium to the onerecording power based on the reliability.

According to the recording/reproduction apparatus, therecording/reproduction method, the program and the recording poweradjustment apparatus of the present invention, a recording power duringrecording is optimized by using a reproduced signal evaluation indexwhich is correlated with decoding performance in a processing systememploying maximum likelihood decoding (PRML) for processing a reproducedsignal. As a result, a recorded state can be optimized and error can beminimized during reproduction. In the present invention, a change inreproduced waveform due to a change in recording power can be detectedwith high precision, as compared to when a reproduced signal qualityindex, such as jitter, asymmetry, BER or the like, which areconventionally used for recording power control is used. Therefore,recording power control can be performed with high precision. Therefore,performance degradation due to cross power can be minimized, resultingin stable compatibility of optical disc drive apparatuses and opticaldisc media having the same standard.

Thus, the invention described herein makes possible the advantages ofproviding a recording/reproduction apparatus, recording/reproductionmethod, program and recording power adjustment apparatus, which have ahigher sensitivity of detection of a degradation in a reproducedwaveform due to deviation of recording conditions and do not require alarge quantity of test writing area; and a recording/reproductionapparatus, recording/reproduction method, program and recording poweradjustment apparatus capable of suppressing a degradation in performancedue to a cross power and having stable compatibility of optical discdrive apparatuses and recording media having the same standard.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a state transition diagram representing a state transitionrule which is defined based on a recording code having a minimumpolarity reversal interval of 2 and an equalization system PR (1, 2, 2,1).

FIG. 2 is a trellis diagram which is obtained by extending the statetransition diagram A along a time axis.

FIGS. 3A and 3B show distributions of Pa−Pb.

FIG. 4 is a diagram showing a recording/reproduction apparatus accordingto an example of the present invention.

FIG. 5 is a diagram showing a recording power learning procedureaccording to Embodiment 1 of the present invention.

FIG. 6 is a diagram showing a plot of an index M for each write powerand determination of an optimum write power Pwo.

FIG. 7 is a diagram showing a test pattern and a waveform when a patternis reproduced.

FIG. 8 is a diagram showing a plot of an index M for each erase powerand determination of an optimum erase power Peo.

FIG. 9 is a diagram showing a plot of an index M for each bottom powerand determination of an optimum bottom power Pbo.

FIG. 10 is a diagram showing a recording/reproduction apparatusaccording to Embodiment 2 of the present invention.

FIG. 11 is a diagram for explaining a relationship among Itop, Ibtm andIth.

FIG. 12 is a diagram showing a relationship between the degree ofmodulation MOD and a write power Pw.

FIG. 13 is a diagram showing a recording/reproduction apparatusaccording to Embodiment 3 of the present invention.

FIG. 14 is a diagram showing a pattern detection circuit and an edgeshift detection circuit.

FIG. 15 is a timing chart showing an operation of an edge shiftdetection circuit.

FIG. 16 shows an example of a recording pattern for learning.

FIG. 17 is a diagram showing an edge shift detection circuit which is amodification of the edge shift detection circuit of FIG. 14.

FIGS. 18A to 18H are diagrams showing sample values of 8 patterns(Pattern-1 through Pattern-8).

FIGS. 19A and 19B are diagrams showing a correlation between areproduction waveform and a shift of a recording mark of Pattern-1 ofFIG. 18A where path A is the correct path.

FIGS. 20A and 20B are diagram showing a correlation between areproduction waveform and a shift of a recording mark of Pattern-1 wherepath B is the correct path.

FIG. 21 is a table showing a list of recording parameters requiringoptimization.

FIG. 22 is a table showing a pattern(s) of particular eight patternswhich is used to detect a recording parameter requiring optimization.

FIG. 23 is a diagram showing an edge shift value (filled triangle) of5Ts5Tm, 5Tm5Ts with respect to a change in power, the absolute value(filled square) of a 5T mark length measured based on an edge shiftvalue (filled circle) of 5Ts5Tm, and an edge shift value of 5Tm5Ts.

FIG. 24 is a diagram showing a multipulse having a write power Pw, anerase power Pe and a bottom power Pb.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings.

1. Index M

Firstly, a reproduced signal evaluation index (index M), which isreferenced in the present invention, will be described. For example, areproduced signal evaluation index M will be described where a recordingcode (e.g., (1, 7) Run Length Limited code) having a minimum polarityreversal interval of 2 is used to shape a signal waveform for PR (1, 2,2, 1) equalization of the frequency Characteristics of a signal during arecording/reproduction operation.

After test recording, a series of digital signals (binary signal “1” or“0”) reproduced from a recording track include a recording code b_(k) atcurrent time k, a recording code b_(k-1) at time k−1 (a unit time beforethe current time), a recording code b_(k-2) at time k−2 (two unit timesbefore the current time), and a recording code b_(k-3) at time k−3(three unit times before the current time). An ideal output valueLevel_(v) of PR (1, 2, 2, 1) equalization is represented by:

Level_(v) =b _(k-3)+2b _(k-2)+2b _(k-1) +b _(k)  (Expression 1)

where k is an integer indicating time and v is an integer of 0 to 6.

A state transition table is show in Table 1 below, where a state at timek is represented by S(b_(k-2), b_(k-1), b_(k)).

TABLE 1 State transition based on a combination of a recording codehaving a minimum polarity reversal interval of 2 and PR (1, 2, 2, 1)State at time k − 1 State at time k S(b_(k−3), b_(k−2), b_(k−2))S(b_(k−2), b_(k−1), b_(k)) B_(k)/Level_(v) S(0, 0, 0) S(0, 0, 0) 0/0S(0, 0, 0) S(0, 0, 1) 1/1 S(0, 0, 1) S(0, 1, 1) 1/3 S(0, 1, 1) S(1, 1,0) 0/4 S(0, 1, 1) S(1, 1, 1) 1/5 S(1, 0, 0) S(0, 0, 0) 0/1 S(1, 0, 0)S(0, 0, 1) 1/2 S(1, 1, 0) S(1, 0, 0) 0/3 S(1, 1, 1) S(1, 1, 0) 0/5 S(1,1, 1) S(1, 1, 1) 1/6

FIG. 1 shows a state transition diagram A where a state S(0, 0, 0)_(k)at time k is represented by S0_(k), a state S(0, 0, 1)_(k) isrepresented by S1_(k), a state S(0, 1, 1)_(k) is represented by S2k, astate S(1, 1, 1)_(k) is represented by S3k, a state S(1, 1, 0)_(k) isrepresented by S4_(k), and a state S(1, 0, 0)_(k) is represented byS5_(k) for the sake of simplicity.

FIG. 1 shows a state transition diagram A representing a statetransition rule which is defined based on a recording code having aminimum polarity reversal interval of 2 and an equalization system PR(1, 2, 2, 1).

FIG. 2 shows a trellis diagram which is obtained by extending the statetransition diagram A along a time axis.

Hereinafter, state transition defined based on a recording code having aminimum polarity reversal interval of 2 and an equalization system PR(1, 2, 2, 1) will be described with reference to FIGS. 1 and 2.

See a state S0_(k) at time k and a state state S0_(k-4) at time k−4.FIG. 2 shows two possible state transition sequences between the stateS0_(k) and the state S0_(k-4). One of the possible state transitionsequences is referred to as a path A. The path A is a transitionsequence of states S2_(k-4), S4_(k-3), S5_(k-2), S0_(k-1) and S0k. Theother state transition sequence is referred to as a path B. The path Bis a transition sequence of states S2_(k-4), S3_(k-3), S4_(k-2),S5_(k-1) and S0_(k). The results of maximum likelihood decoding fromtime _(k-6) to time _(k) is represented by (C_(k-6), C_(k-5), C_(k-4),C_(k-3), C_(k-2), C_(k-1), C_(k)). In this case, when the decodingresult (C_(k-6), C_(k-5), C_(k-4), C_(k-3), C_(k-2), C_(k-1), C_(k)) is(0, 1, 1, x, 0, 0, 0) where x is 0 or 1, it is estimated that the statetransition sequence of the path A or the path B is most probable. Thepath A and the path B have the same probability that a state at time k−4is the state S2_(k-4). Therefore, by calculating a value of sum ofsquares of differences between a reproduced signal y_(k-3) to areproduced signal y_(k) and corresponding expected values on each of thepath A and the path B from time k−3 to time k, it is determined whetherthe transition sequence of the path A or the path B is probable.

The value of the sum of squares of differences between a reproducedsignal y_(k-3) to a reproduced signal y_(k) and corresponding expectedvalues on the path A from time k−3 to time k, is represented by Pa. Pais represented by:

Pa=(y _(k-3)−4)²+(y _(k-2)−3)²+(y _(k-1)−1)²+(y _(k)−0)²  (Expression 2)

The value of the sum of squares of differences between a reproducedsignal y_(k-3) to a reproduced signal y_(k) and corresponding expectedvalues on the path B from time k−3 to time k, is represented by Pb. Pbis represented by:

Pb−(y _(k-3)−5)²+(y _(k-3)−5)²+(y _(k-3)−3)²+(y _(k)−1)²  (Expression 3)

Hereinafter, the meaning of the difference Pa and Pb (i.e., Pa−Pb) willbe described where Pa and Pb indicate the reliability of the result ofmaximum likelihood decoding. A maximum likelihood decoding sectionselects the path A with high confidence if Pa<<Pb, and the path B ifPa>>Pb. If Pa=Pb, either the path A or the path B is selected. In thiscase, the chance that the decoding result is true is fifty-fifty. Thus,a distribution of Pa−Pb is obtained based on a predetermined time or apredetermined number of times and the decoding result.

FIGS. 3A and 3B show distributions of Pa−Pb.

FIG. 3A, shows a distribution of Pa−Pb when noise is added to areproduced signal. The distribution has two peaks. One of the peaksindicates a maximum incidence when Pa=0, while the other indicatesanother maximum incidence when Pb=0. The value of Pa−Pb when Pa=0 isrepresented by −Pstd, while the value of Pa−Pb when Pb=0 is representedby Pstd. The absolute value of Pa−Pb is calculated and |Pa−Pb|-Pstd isobtained.

FIG. 3B shows a distribution of |Pa−Pb|−Pstd. The standard deviation aand the average Pave of the distribution of FIG. 38 are calculated. Itis assumed that the distribution of FIG. 3B is a normal distribution.For example, it is also assumed that error occurs when the value of|Pa−Pb|, which is the reliability of a decoding result is equal to orless than −Pstd. An error probability based on P (σ, Pave) isrepresented by:

P(σ, Pave)=erfc((Pstd+Pave)/σ).  (Expression 4)

The error rate of a binary signal indicating the result of maximumlikelihood decoding can be predicted based on the average Pave and thestandard deviation σ of the distribution of Pa−Pb. In other words, theaverage Pave and the standard deviation σ can be used as indexes for thequality of a reproduced signal.

In the above example, the distribution of |Pa−Pb| is assumed to be anormal distribution. In the case where the distribution is not a normaldistribution, the number of times that the value of |Pa−Pb|−Pstd is lessthan or equal to a predetermined reference value is counted. Theobtained number of counts can be an index of the quality of thereproduced signal.

In the case of the state transition rule defined by the recording codehaving a minimum polarity reversal interval of 2 and the equalizationsystem PR (1, 2, 2, 1), there are two possible state transition paths inthe following number of state transition patterns: 8 patterns from timek−4 to time k; 8 patterns from time k−5 to time k; and 8 patterns fromtime k−6 to time k. In a wider range of detection, there are Pa−Pbpatterns, where Pa−Pb is the level of reliability.

Among a number of patterns, there are a number of patterns which areinsensitive to a change in a recording parameter (e.g., a write power,an erase power, etc.). For example, such a pattern is a path involved ina change in a space for a long mark or a mark portion. By selecting onlya pattern, which responds sensitively to a recording parameter, exceptfor the above-described pattern, it is possible to detect a change in areproduced waveform with respect to a change in a recording parameter (arecording power) with high precision. A pattern highly sensitive to therecording parameter is shown in Table 2.

TABLE 2 Patterns in which there can be two shortest state transitionpaths Reliability of decoding result (pa-pb) State transition Pa = 0 Pb= 0 S2_(k−4) → S0_(k) −10 +10 S3_(k−4) → S0_(k) −10 +10 S2_(k−4) →S1_(k) −10 +10 S3_(k−4) → S1_(k) −10 +10 S0_(k−4) → S4_(k) −10 +10S5_(k−4) → S4_(k) −10 +10 S0_(k−4) → S3_(k) −10 +10 S5_(k−4) → S3_(k)−10 +10

Specifically, a pattern group in Table 2 is involved in a transitionwaveform from a mark to a space or a space to a mark. For example,portions which respond sensitively to the power of a recording leadingpulse (write power), the power of a cooling pulse (bottom power), or theratio of a write power/an erase power, are grouped.

It is preferable to use the reliability Pa−Pb as an index of the qualityof the reproduced signal. In this case, it is not necessary to detectall the patterns. By only detecting a pattern(s) having a high errorprobability, such a detection result can be used as an index which iscorrelated with the error, probability. A pattern having a high errorprobability is a pattern having a small value of reliability Pa−Pb.There are 8 such patterns, where Pa−Pb=±10. These 8 patterns and Pa−Pbare summarized in Table 2 above.

Further, |Pa−Pb|−Pstd is calculated. A standard deviation σ₁₀ and anaverage Pave₁₀ are calculated from the distribution. As described withreference to FIG. 38, if the distribution is assumed to be a normaldistribution, a probability P₁₀ of occurrence of error is representedby:

P ₁₀(σ₁₀, Pave₁₀)=erfc((10+Pave₁₀)/σ₁₀).  (Expression 5)

In the above-mentioned 8 patterns, a 1-bit shift error occurs. In theother patterns, a 2- or more bit shift error occurs. A result ofanalysis of post-PRML processing error patterns shows that most of theerrors are 1-bit shift errors. Therefore, the error probability of thereproduced signal can be estimated by expression 6. In this manner, thestandard deviation σ₁₀ and the average value Pave₁₀ can be used as anindex of the quality of the reproduced signal. For example, thefollowing expression can be defined, assuming that the above-describedindex is a PRML error index M:

M=σ10/(2·d _(min) ²) [%]  (Expression 6)

where d_(min) ² is the square of a minimum value of a Euclid distance,which is equal to 10 when a modulation code having a minimum polarityreversal interval of 2 and the PR (1, 2, 2, 1) ML system are combined.In other words, d_(min) ²=10=Pstd. Note that the average Pave₁₀ inexpression 5 is assumed to be 0 and is not taken into account when theindex of expression is calculated. Based on the relationship betweenexpressions 5 and 6, the error rate after PRML processing can bepredicted using the index M.

Thus, by detecting a state, which is recorded using a metric expectedvalue error of only a state transition pattern (a pattern with theminimum Euclid distance) involved in the vicinity of an edge of areproduced waveform among a number of state transition patterns in thePRML algorithm, the index M can be detected with high precisionirrespective of variations in the power of a recording leading pulse(write power), the power of a cooling pulse (bottom power), or the ratioof a write power/an erase power.

2. Embodiment 1 2-1. Recording/Reproduction Apparatus of Embodiment 1

FIG. 4 shows a recording/reproduction apparatus 100 according to anexample of the present invention. The recording/reproduction apparatus100 includes a reproduction section 101, a recording control device 102,and a recording section 103. On the recording/reproduction apparatus100, a recording medium 1 can be mounted. A recording medium 1 is usedfor optical information recording and reproduction, and is, for example,an optical disc.

The reproduction section 101 includes an optical head section 2, apreamplifier 3, an AGC 4, a waveform equalizer 5, an A/D converter 6,and a PLL circuit 7. The reproduction section 101 generates a digitalsignal from an analog signal representing information reproduced fromthe recording medium 1.

The recording control section 102 includes a shaping section 8, amaximum likelihood decoding section 9, a reliability calculation section10, and a recording medium controller 11. The recording control section102 is produced as, for example, a semiconductor chip.

The shaping section 8 is, for example, a digital filter, and receives adigital signal generated by the reproduction section 101 and shapes thewaveform of the digital signal such that the digital signal has apredetermined equalising characteristic.

The maximum likelihood decoding section 9 is, for example, a Veterbidecoding circuit, and performs maximum likelihood decoding of thedigital signal having the waveform thereof shaped by the shaping section8 and generates a binary signal representing the result of the maximumlikelihood decoding.

The reliability calculation section 10 is, for example, a differentialmetric detection circuit, and calculates the reliability of the resultof maximum likelihood decoding based on the digital signal having thewaveform thereof shaped by the shaping section 8 and the binary signaloutput from the maximum likelihood decoding section 9.

The recording medium controller 11 adjusts a recording power forrecording information onto the recording medium 1 based on a reliabilitycalculated by the reliability calculation section 10. For example, therecording power to be adjusted includes at least one of a write power,an erase power, and a bottom power. The recording medium controller 11adjusts the shape of a recording signal in a manner which allows theresult of maximum likelihood decoding to have a higher level ofreliability. The recording medium controller 11 is, for example, anoptical disc controller.

The recording section 103 includes a recording signal generation section12, a recording power control section 13, a laser drive circuit 14, andan optical head 2. The recording section 103 records information ontothe recording medium 1 based on the result of adjustment of a recordingpower.

In this example, the optical head 2 is shared by the reproductionsection 101 and the recording section 103, and functions as both arecording head and a reproduction head. The recording head and thereproduction head may be separately provided.

Hereinafter, an operation of the recording/reproduction apparatus 100will be described in detail with reference to FIG. 4.

The optical head section 2 generates an analog reproduced signalrepresenting information which is read from the recording medium 1. Theanalog reproduced signal is amplified and AC-coupled by the preamplifier3 and then is input to the AGC 4. The AGC 4 adjusts the gain of theanalog reproduced signal such that the output from the waveformequalizer 5, which will later process the signal, has a constantamplitude. The analog reproduced signal which is output from the AGC 4has the waveform thereof shaped by the waveform equalizer 5. Theresultant analog reproduced signal is output to the A/D converter 6. TheA/D converter 6 samples the analog reproduced signal in synchronizationwith a reproduction clock which is output from the PLL circuit 7. ThePLL circuit 7 extracts the reproduction clock from a digital reproducedsignal obtained by sampling performed by the A/D converter 6.

The digital reproduced signal generated by sampling performed by the A/Dconverter 6 is input to the shaping section 8. The shaping section 8adjusts the frequency characteristics of the digital reproduced signal(i.e. adjusts the waveform of the digital reproduced signal), such thatthe frequency characteristics of the digital reproduced signal are thecharacteristics assumed by the maximum likelihood decoding section 9 (inthis example, PR (1, 2, 2, 1) equalization characteristics) at the timeof recording and reproduction.

The maximum likelihood decoding section 9 performs maximum likelihooddecoding of the digital reproduced signal having the waveform thereofshaped by the shaping section 8, and thus generates at least one binarysignal. The at least one binary signal indicates the result of maximumlikelihood decoding.

The reliability calculation section 10 receives at least one digitalreproduced signal having the waveform thereof shaped by the shapingsection 8 and at least one binary signal. The reliability calculationsection 10 identifies state transition from the binary signal, and theindex M based on the identification result and a branch metric.

The recording medium controller 11 controls a recording power learningprocedure. In the procedure, recording power parameters are set for testrecording, a recording operation is controlled, a reproduction operationis controlled, an index M is calculated for each recording power, and arecording power is determined so that the index M is optimized. Thedetails of the recording power learning procedure will be describedbelow.

The recording power control section 13 generates a laser light waveformbased on a recording power parameter output from the recording mediumcontroller 11 and a recording test pattern output from the recordingsignal generation section 12. The laser drive circuit 14 drives theoptical head 2 to emit laser in accordance with the laser light pattern.

By using the recording/reproduction apparatus 100, it is possible toestablish an optimum write power, an erase power and a bottom power,which minimize error during reproduction.

2-2. Recording/Reproduction Method of Embodiment 1

FIG. 5 shows a recording power learning procedure according toEmbodiment 1 of the present invention. The recording/reproductionapparatus 100 performs the recording power learning procedure to adjusta recording power. The recording power learning procedure comprisessteps 1 to 3.

Hereinafter, the recording power learning procedure will be describedstep by step with reference to FIG. 5.

When the recording power learning is started, an optimum write power Pwois calculated in step 1. Step 1 includes steps 1-1, 1-2 and 1-3.

Step 1-1: The optical head 2 is controlled to be shifted into apredetermined learning area on the recording medium 1. An erasepower/write power ratio (Pe/Pw) and a bottom power are fixed. A testrecording signal is written while changing a write power sequentially.In this case, the erase power/write power ratio and the bottom power maybe fixed to recommended values previously recorded on the recordingmedium 1, which are defined in accordance with a standard or the like,as initial values. The write power may be changed around a recommendedvalue previously recorded on the recording medium 1.

Alternatively, recommended values which the recording/reproductionapparatus 100 stores for each recording medium may be used as initialvalues. For example, it is assumed that the recommended valuespreviously recorded on the recording medium 1 are Pw=9.0 [mW],Pe/Pw=0.40, and Pb=0.3 [mW]. In this case, Pe/Pw and Pb are fixed to0.40 and 0.3, respectively. While Pw is changed from 8.0 to 10.0 [mW] by0.2 [mW], the same test recording signal is repeatedly recorded for eachwrite power.

After test recording, the procedure goes to step 1-2.

Step 1-2: The optical head 2 reproduces the recorded test recordingsignal. The reliability calculation section 10 calculates a recordedstate determination index value for each write power. As described above(1. Index M), the present invention is characterized in that a metricexpected value error (hereinafter referred to as an index M) of the PRMLtechnique extracted from state transition corresponding to the vicinityof an edge of a reproduced waveform is used as a recorded statedetermination index value. Features of the index M are that the index Mis correlated with an error rate in a transmission path which employsthe PRML technique for processing of a reproduced signal, that the indexM can be detected with high sensitivity to the asymmetry of a waveformdue to a change in power, and the like.

After the reliability calculation section 10 calculates a recorded statedetermination index value for each write power, the procedure goes tostep 1-3.

Step 1-3: the reliability calculation section 10 determines a writepower, which allows an optimum index M, as an optimum write power Pwo.For example, the reliability calculation section 10 selects a minimumvalue as an optimum index M, and determines a write power correspondingto the selected index M as an optimum write power Pwo.

For example, FIG. 6 shows a plot of an index M for each write power anddetermination of an optimum write power Pwo.

FIG. 7 shows a test pattern and a waveform when the pattern isreproduced. Open circles on the reproduced waveform indicate samplingpoints obtained by the A/D converter 6. The present invention is alsocharacterized by the test recording signal. Conventionally, a singlepattern having a predetermined cycle is used as a test pattern forrecording power learning. For example, such a single pattern is a repeatpattern of 6T (T is a channel cycle). The single pattern resistsinfluences of width or phase shift of a recording pulse for eachrecording mark length. However, a change in waveform corresponding to achange in recording power may be detected with less precision. In thepresent invention, in a recording modulation rule, a minimum mark lengthand a maximum mark length are combined, and a test pattern in which arecorded portion (mark) and an unrecorded portion (space) occur with thesame probability is used. For example, when the (1, 7) Run LengthLimited code is used as a recording modulation code, the minimum marklength is 2T and the maximum mark length is 8T, a repeat pattern of8Tm2Ts8Tm8Ts2Tm8Ts is used. Tm indicates a channel cycle length of marksand Ts indicates a channel cycle length of spaces.

Thus, in step 1, a write power which allows an optimum index M, isdetermined as an optimum write power Pwo.

Thereafter, in step 2, an optimum erase power Peo is obtained. Step 2includes steps 2-1, 2-2 and 2-3.

In step 2-1: The recording medium controller 11 sets a write power tothe optimum write power Pwo determined in step 1. Further, the recordingmedium controller 11 fixes a bottom power, and writes a test recordingsignal (test recording) while changing an erase power sequentially.

For example, Pw and Pb are fixed to 9.4 [mW] (Pwo) and 0.3 [mW],respectively. While Pe is changed from 3.4 to 4.1 [mW] by 0.1 [mW] wherethe center is Pe=Pw*0.4=3.76 [mW], the same test recording signal isrepeatedly recorded for each write power. The recording can be performedby overwriting a track having a previously recorded state.Alternatively, the same track as that used in step 1 can be used.

After writing of a test recording signal (test recording) is ended, theprocedure goes to step 2-2.

Step 2-2: The optical head 2 reproduces the recorded test recordingsignal. The reliability calculation section 10 calculates a recordedstate determination index value (index M) for each erase power.

The index M is used as a recorded state determination index as instep 1. A repeat pattern of 8Tm2Ts8Tm8Ts2Tm8Ts is used as a testrecording signal.

After the reliability calculation section 10 calculates a recorded statedetermination index value for each erase, power, the procedure goes tostep 2-3.

Step 2-3: The reliability calculation section 10 determines an erasepower, which allows an optimum index M, as an optimum erase power Peo.The reliability calculation section 10 selects, for example, a minimumvalue as the optimum index M, and an erase power corresponding to theselected index M as an optimum erase power Peo.

For example, FIG. 8 shows a plot of an index M for each erase power anddetermination of an optimum erase power Peo.

Thereafter, in step 3, an optimum bottom power Pbo is calculated. Step 3includes steps 3-1, 3-2 and 3-3.

Step 3-1: The recording medium controller 11 sets a write power to theoptimum write power Pwo determined in step 1. The recording mediumcontroller 11 sets an erase power to the optimum erase power Peodetermined in step 2. Further, the recording medium controller 11 writesa test recording signal while changing a bottom power sequentially (testrecording).

For example, Pw and Pe are fixed to Pwo=9.4 [mW] and Peo=3.9 [mW],respectively. While Pb is changed from 0.2 to 0.4 [mW] by 0.05 [mW], thesame test recording signal is repeatedly recorded for each write power.The recording can be performed by overwriting a track having apreviously recorded state. Alternatively, the same track as that used insteps 1 and 2 can be used for recording.

After writing of a test recording signal (test recording) is ended, theprocedure goes to step 3-2.

Step 3-2: The optical head 2 reproduces the recorded test recordingsignal. The reliability calculation section 10 calculates a recordedstate determination index value (index M) for each bottom power. Theindex M is used as a recorded state determination index as in steps 1and 2. A repeat pattern of 8Tm2Ts8Tm8Ts2Tm8Ts is used as a testrecording signal.

After the reliability calculation section 10 calculates a recorded statedetermination index value for each bottom power, the procedure goes tostep 3-3.

Step 3-3: the reliability calculation section 10 determines a bottompower obtained from an optimum index M as an optimum bottom power Pbo.The reliability calculation section 10 selects a minimum value as theoptimum index M and determines a bottom power corresponding to theselected index M as an optimum bottom power Pbo.

For example, FIG. 9 shows a plot of an index M for each bottom power anddetermination of an optimum bottom power Pbo.

As described above, by performing steps 1 to 3, the learning procedurefor establishing an optimum write power, erase power and bottom power isended and recording can be performed with minimum error duringreproduction. Note that when a change in bottom power has substantiallyno influence on readability during reproduction, learning in step 3 maybe omitted and a bottom power may be set to an appropriate fixed value.

As described above, in Embodiment 1 of the present invention, bydetecting a state, which is recorded using a metric expected value errorof only a state transition pattern (a pattern with the minimum Eucliddistance) involved in the vicinity of an edge of a reproduced waveformamong a number of state transition patterns in the PRML algorithm, arecorded waveform changed corresponding to variations in the power of arecording leading pulse (write power), the power of a cooling pulse(bottom power), or the ratio of a write power/an erase power, can bedetected with high precision. A repeat pattern of 8Tm2Ts8Tm8Ts2Tm8Ts isused as a test pattern, taking into account that it resists theinfluence of the width or phase shift of a recording pulse for eachrecording mark length, that a change in waveform corresponding to achange in recording power is detected with high sensitivity, and thelike. As a result, the detection sensitivity can be further improved.

3. Embodiment 2 3-1. Recording/Reproduction Apparatus of Embodiment 2

FIG. 10 shows a recording/reproduction apparatus 200 according toEmbodiment 2 of the present invention. The recording/reproductionapparatus 200 comprises a recording control device 202 instead of therecording control device 102 of the recording/reproduction apparatus 100according to Embodiment 1 of the present invention, which is describedwith reference to FIG. 4. Therefore, in FIG. 10, the same parts as thoseof the recording/reproduction apparatus 100 of FIG. 4 are referencedwith the same reference numerals and will not be explained.

The recording control device 202 comprises a shaping section 8, amaximum likelihood decoding section 9, a reliability calculation section10, a recording medium controller 11, and the modulation degreedetection circuit 15. The recording control device 202 is produced as,for example, a semiconductor chip.

The modulation degree detection circuit 15 calculates modulation degreecharacteristics based on an amplitude of a reproduced signal read fromthe optical head section 2, and outputs the modulation degreecharacteristics to the recording medium controller 11.

The recording medium controller 11 adjusts a recording power forrecording information onto a recording medium 1 based on at least one ofreliability and modulation degree characteristics.

As described above, the recording/reproduction apparatus 200 establishesan optimum write power, erase power and bottom power which allow minimumerror during reproduction.

3-2. Recording/Reproduction Method of Embodiment 2

Hereinafter, a recording power learning procedure according toEmbodiment 2 of the present invention will be described with referenceto FIG. 5. The recording/reproduction apparatus 200 performs a recordingpower learning procedure to adjust a recording power.

In Embodiment 2 of the present invention, the same steps as those inEmbodiment 1 will not be explained. As in Embodiment 1, the recordingpower learning procedure of Embodiment 2 comprises steps 1 to 3. In thestep of calculating an optimum write power Pwo (step 1), the degree ofmodulation is used as a recorded state determination index value, as isdifferent from Embodiment 1. The details of the step of calculating anoptimum write power Pwo based on the degree of modulation will bedescribed below.

In step 1, the degree of modulation is obtained for each of setting of arecording power parameter for test recording, control of a recordingoperation, control of a reproduction operation, and a recording power.The reliability calculation section 10 determines an optimum write powerPwo based on the calculated degree of modulation.

Similarly, in steps 2 and 3, an index M is obtained for each of settingof a recording power parameter for test recording, control of arecording operation, control of a reproduction operation, and arecording power. The reliability calculation section 10 determines anoptimum erase power Peo and an optimum bottom power Pbo based on theindex M.

Hereinafter, the step of determining an optimum write power Pwo based onthe degree of modulation will be described.

The degree of modulation is an index indicating the size of an amplitudeof a reproduced signal. The degree of modulation MOD is defined based onexpression 7.

MOD=(Itop−Ibtm)/(Itop−Ith)  (Expression 7)

FIG. 11 is a diagram for explaining a relationship among Itop, Ibtm andIth.

Hereinafter, Itop, Ibtm and Ith contained in expression 7 will bedescribed with reference to FIG. 11.

Itop indicates a highest reflection level of a reproduced signal. Ibtmindicates a lowest reflection level of a reproduced signal. Ithindicates a level of laser erase light. In this embodiment, the degreeof modulation is used to obtain an 8T-repeat signal. The presentinvention is not limited to this.

FIG. 12 shows a relationship between the degree of modulation MOD and awrite power Pw.

The degree of modulation MOD varies depending on the write power Pw.When the write power Pw is low, the amplitude of a reproduced signal islow, so that the degree of modulation MOD is small. As the write powerPw is increased, the amplitude of a reproduced signal is increased, sothat the degree of modulation MOD is increased. When the write power Pwis increased to a predetermined extent, the degree of modulation MOD issaturated.

A tangent of a modulation degree curve is obtained with reference to aportion thereof in which the write power Pw is relatively low (severalsamples from a non-saturated portion). An intersection Pth between thetangent and the X axis is obtained (see FIG. 12). A coefficient ρ forobtaining an optimum write power Pwo from Pth is previously recorded ona disc or is stored in a recording/reproduction apparatus for each disc.The coefficient ρ is used to calculate an optimum write power Pwo inaccordance with the following expression.

Pwo=ρ×Pth  (Expression 8)

Thus, in step 1, the optimum write power Pwo is determined based on themodulation degree characteristics.

In steps 2 and 3, the step of determining an optimum erase power Peo anda bottom power Pbo is the same as that of Embodiment 1 and will not beexplained. When a change in bottom power has substantially no influenceon readability during reproduction, step 3 may be omitted and the bottompower may be fixed to an appropriate value.

In Embodiment 2, expression 8 is referenced when determining Pwo usingthe degree of modulation. The present invention is not limited to this.For example, a power with which a predetermined degree of modulation isdetected may be regarded as Pwo. Alternatively, a power with which thedegree of modulation is saturated may be regarded as Pwo.

In Embodiment 2, a test signal includes a repeat pattern of ETWITs. Thepresent invention is not limited to this. A test signal only needs tocontain a pattern in which the upper and lower amplitudes of areproduced signal can be measured.

4. Embodiment 3 4-1. Recording/Reproduction Apparatus of Embodiment 3

FIG. 13 shows a recording/reproduction apparatus 300 according toEmbodiment 3 of the present invention. The recording/reproductionapparatus 300 comprises a recording control device 302 instead of therecording control device 102 included in the recording/reproductionapparatus 100 of Embodiment 1 of the present invention, which isdescribed with reference to FIG. 4, and a recording section 303 insteadof the recording section 103 included in the recording/reproductionapparatus 100. Therefore, in FIG. 13, the same parts as those of therecording/reproduction apparatus 100 of FIG. 4 are referenced with thesame reference numerals and will not be explained.

The recording control device 302 comprises a shaping section 8, amaximum likelihood decoding section 9, a reliability calculation section10, and a control section 304 (a pattern detection circuit 3.7, an edgeshift detection circuit 18, and a recording medium controller 11). Therecording control device 302 is fabricated as, for example, asemiconductor chip.

The reliability calculation section 10 is, for example, a differentialmetric detection circuit, and calculates the reliability of the resultof the maximum likelihood decoding based on the digital signal havingthe waveform thereof shaped by the shaping section 8 and the binarysignal output from the maximum likelihood decoding section 9. In oneembodiment of the present invention, the reliability calculation section10 calculates the reliability of the result of the maximum likelihooddecoding based on digital signals corresponding to a mark start edge anda mark termination edge of a recording mark formed on the recordingmedium 1 and binary signals.

The adjusting section 304 adjusts the shape of predetermined portions ofa recording signal for recording information on the recording medium 1based on the reliability calculated by the reliability calculationsection 10. The adjusting section 304 adjusts, for example, thepositions of edges of the recording signal. The adjustment of the shapeof the recording signal by the adjusting section 104 is performed suchthat the reliability of the result of the maximum likelihood decoding isimproved. The recording medium controller 11 is, for example, an opticaldisc controller.

The recording section 303 includes a pattern generation circuit 14, arecording compensation circuit 15, a laser driving circuit 16, and anoptical head section 2. The recording section 303 records information onthe recording medium 1 based on the adjusting result of the shape of therecording signal. In this example, the optical head section 2 isincluded both in the reproduction section 101 and the recording section303, and functions as both a recording head and a reproduction head. Therecording head and the reproduction head may be separately provided.

An operation of the recording/reproduction apparatus 300 will bedescribed in detail below. The operation of the same parts as those ofthe recording/reproduction apparatus 100 will not be explained.

Based on the binary signal, the pattern detection circuit 17 generates apulse signal for assigning the above-mentioned 8 patterns (Pattern-1through Pattern-8) for each recording pattern, and outputs the pulsesignal to the edge shift detection circuit 18.

The edge shift detection circuit 18 accumulatively adds the reliabilityPabs pattern by pattern, and obtains a shift of the recordingcompensation parameter from the optimum value (i.e., an edge shift).

The recording medium controller 11 changes a recording parameter (thewaveform of a recording signal) which it is determined that needs to bechanged based on the edge shift amount for each pattern.

The pattern generation circuit 14 outputs a recording compensationleaning pattern.

Based on the recording parameter from the recording medium controller11, the recording compensation circuit 15 generates a laser lightwaveform pattern in accordance with the recording compensation leaningpattern. In accordance with the resultant laser light waveform pattern,the laser driving circuit 16 controls a laser light emission operationof the optical head section 2.

FIG. 14 shows the pattern detection circuit 17 and the edge shiftdetection circuit 18.

Hereinafter, an operation of the edge shift detection circuit 18 will bedescribed in detail with reference to FIG. 14.

The edge shift detection circuit 18 receives a pattern detection resultobtained by the pattern detection circuit 17 and the reliability Pabscalculated by the reliability calculation section 10. The reliabilityPabs data input to the edge shift detection circuit 18 is delayed by aflip-flop (FF) in consideration of the delay caused by the patterndetection circuit 17. The reliability Pabs data corresponding to thepattern detection output and the detection output point are input to anadder, and the pattern detection result is input to a selector. Theselector selects the accumulation result obtained up to that point inaccordance with the detection pattern and inputs the selected result tothe adder. The adder adds the accumulation result and the newly inputreliability Pabs data, and outputs the addition result. A specificregister corresponding to the detection pattern, when receiving anenable signal, stores the addition result.

FIG. 15 is a timing chart showing an operation of the edge shiftdetection circuit 18. For example, in the case where information isrecorded on a recording medium in which information is managed addressby address, it is assumed to use an addition interval gate signal ((b)of FIG. 15) and a register enable signal ((c) of FIG. 15). Part (a) ofFIG. 15 shows an address unit.

In the case where test recording is performed in a user area address byaddress so as to obtain an edge shift amount, a control needs to beperformed for defining an addition interval. When the addition intervalgate signal is input to the edge shift detection circuit 18, theaddition interval gate signal passes through the two-stage flip-flop andis input to flip-flops FF29 through FF0 (FIG. 14). The flip-flops arereset in a low interval of the addition interval gate signal, and theaddition result is stored in a high interval. The register enable signalis generated from the addition interval gate signal. The register enablesignal is for storing the addition result to registers REG29 throughREG0 at the end of the addition interval gate signal.

Data representing the edge shift amount address by address is stored inthe registers REG29 through REG0. The edge shift detection circuit 18,owing to such a circuit configuration, can obtain all the edge shiftamounts necessary for optimization of the recording parameter using oneadder.

In the exemplary circuit described with reference to FIG. 14, thegeneration frequency of the recording patterns varies in accordance withthe combination of the predetermined length of marks and spaces requiredfor optimization of the recording parameter, among the recordingpatterns used for test recording (e.g., random patterns). The 30 edgeshift amounts detected (R23T, R33T, R45L, R55L) rely on the incidence ofthe recording patterns. The PLL circuit 7 shown in FIG. 1 automaticallydetects a threshold value of a slicer (not shown) using a DC component(a low frequency component included in the reproduced signal) andsynchronizes the reproduced signal and the reproduction clock signal.Accordingly, it is preferable that the amount of the DC componentincluded in the test recording pattern is as small as possible, suchthat the feedback control does not influence the clock generationperformed by the PLL circuit 7. In consideration of the time requiredfor optimization and precision of optimization, it is preferable toobtain a detection result having a high precision with a minimumpossible recording area. Therefore, the following recording pattern isrequired: a recording pattern which has mark length/space lengthcombinations required for optimization of the recording parameter at thesame frequency, in which the code includes no DC component (DSV), and inwhich the generation frequency, per unit area, of the mark length/spacelength combinations required for optimization of the recording parameteris high.

FIG. 16 shows an example of a recording pattern for learning. 2Mrepresents a 2T mark, and 2S represents a 2T space. In this example,each of 30 patterns of combinations of 2T through 5T marks and 2Tthrough 5T spaces is generated once in a 108-bit recording pattern. Thenumber of codes “0” and the number of codes “1” including the 108-bitrecording pattern are both 54, and the DSV in the recording pattern is0. By applying this recording pattern to the edge shift detectioncircuit 18 in FIG. 13, each pattern can be detected the same number oftimes. Thus, a more accurate shift amount detection result is obtained.In this example, it is assumed that 5T or longer marks or 5T or longerspaces can be recorded with the same recording parameter.

FIG. 17 shows an edge shift detection circuit 18 a which is amodification of the edge shift detection circuit 18.

The pattern detection circuit 17 detects an edge of each of specificpatterns (30 patterns). The edge shift detection circuit 18 aaccumulates the edge shift amounts corresponding to each of thepatterns, and counts the number of times that each pattern has beendetected. By dividing each accumulation result of the edge shift amountswith the number of times that the respective pattern has been detected,the average edge shift amount of each specific pattern is obtained.Thus, even when random patterns are used for test recording, it can bedetermined which is the pattern corresponding to the recording markhaving the mark start edge position or the mark termination edgeposition which should be changed.

As described above, the edge shift detection circuit 18 included in theadjusting section 304 calculates one of an accumulation value or anaverage value of the reliability of the maximum likelihood decodingresult for each recording pattern (i.e., for each mark length/spacelength combination), and adjusts the shape of the recording signal basedon the accumulation value or average value obtained.

In the above example, the state transition rule defined by the recordingcode having a minimum polarity inversion interval of 2 and theequalization system of PR (1, 2, 2, 1) is used by the maximum likelihooddecoding section 9 for performing maximum likelihood decoding. Thepresent invention is not limited to this. The present invention isapplicable to use of, for example, a state transition rule defined bythe recording code having a minimum polarity inversion interval of 3 andthe equalization system of PR (C0, C1, C1, C0), a state transition ruledefined by the recording code having a minimum polarity inversioninterval of 2 or 3 and the equalization system of PR (C0, C1, C0), and astate transition rule defined by the recording code having a minimumpolarity inversion interval of 2 or 3 and the equalization system of PR(C0, C1, C2, C1, C0). C0, C1 and C2 are each an arbitrary positivenumeral.

4-2. Recording/Reproduction Method of Embodiment 3

In this example of the present invention, the above-mentioned 8 patternsare detected for each recording pattern (for each combination of a marklength and a space length immediately before the mark, and for eachcombination of a mark length and a space length immediately after themark). A recording parameter for optimizing the position of the edge ofthe recording signal is determined, with specific attention paid to theshape of the recording signal, especially the mark start edge and themark termination edge.

Paying attention only to the pattern having the minimum |Pa−Pb| value,among the reliability |Pa−Pb| of all the maximum likelihood decodingresults of all the patterns, means to pay attention only to the edge ofa recording mark. As described above, a pattern having a small value ofPa−Pb has a high error probability. This means that by partiallyoptimizing the position of the edge of a recording mark so as to improvethe reliability of the maximum likelihood decoding result, the entirerecording parameter is optimized. A method for optimizing the positionof the edge of a recording mark will be described hereinafter.

FIGS. 18A to 18H show sample values of 8 patterns (Pattern-1 throughPattern-8). The horizontal axis represents time. One scale representsone channel clock period (Tclk). The vertical axis represents signallevel (0 through 6). The dotted line represents path A, and the solidline represents path B. Each sample value corresponds to the expectedvalue Level_(v) 0 through 6 of the maximum likelihood decoding describedabove with reference to Table 1.

A recorded portion (amorphous area) is represented as having a signallevel below the threshold value of the comparator since the light amountreflected by the recorded portion is lower than the light amountreflected by the other portions. An unrecorded portion (non-amorphousarea) is represented as having a signal level above the threshold valueof the comparator. The 8 patterns each correspond to a reproductionwaveform of a border (mark start edge or mark termination edge) betweenthe recorded portion (mark) and an unrecorded portion (space). Pattern-1(FIG. 18A), Pattern-2 (FIG. 18B), Pattern-3 (FIG. 18C), and Pattern-4(FIG. 18D) each correspond to a mark start edge. Pattern-5 (FIG. 188),Pattern-6 (FIG. 18F), Pattern-7 (FIG. 18G), and Pattern-8 (FIG. 18H)each correspond to a mark termination edge.

A method for detecting a shift of the mark start edge will be describedusing Pattern-1 as an example.

FIGS. 19A and 19B show the correlation between the reproduction waveformand the shift of a recording mark of Pattern-1. In FIGS. 19A and 19B, anopen triangle represents an input signal. Path A represented by thedotted line is a correct state transition path. The input signal isgenerated based on a recording mark B₁. A recording mark A₁ has an idealposition of the mark start edge.

In FIG. 19A, the position of the mark start edge of the recording markB₁ is behind the ideal position. The sample value of the input signal(y_(k-3), y_(k-2), y_(k-1), y_(k)) is (4.2, 3.2, 1.2, 0.2) . Fromexpressions 2 and 3, a distance Pa between the path A and the inputsignal, and a distance Pb between the path B and the input signal, areobtained by expressions 9 and 10, respectively.

Pa=(4.2−4)²+(3.2−3)²+(1.2−1)²+(0.2−0)²=0.16  (Expression 9)

Pb=(4.2−5)²+(3.2−5)²+(1.2−3)²+(0.2−1)²=7.76  (Expression 10)

The amount and direction of the shift of the mark start edge areobtained by finding |Pa−Pb|−Pstd by expression 9.

E1=|Pa−Pb|−Pstd=|0.16−7.76|−10=−2.4  (Expression 11)

The absolute value of E1 obtained by expression 11 is the shift amount,and the sign of E1 is the shift direction. In the case of the recordingmark B₁ in FIG. 19A, E1=−2.4. This means that the position of the markstart edge of the recording mark B₁ is shifted rearward from thereference by 2.4.

In FIG. 19B, the position of the mark start edge of the recording markB₁ is advanced to the ideal position. The sample value of the inputsignal (y_(k-3), y_(k-2), y_(k-1), y_(k)) is (3.8, 2.8, 0.8, −0.2). E2is obtained by E2=|Pa−Pb|−Pstd. E2 is 2.4. This means that the positionof the mark start edge of the recording mark B1 is shifted forward fromthe reference by 2.4.

FIGS. 20A and 208 show the correlation between the reproduction waveformand the shift of a recording mark of Pattern-1. In FIGS. 20A and 20B,path B represented by the solid line is a correct state transition path.

In FIG. 20A, the position of the mark start edge of the recording markB1 is behind the ideal position. The sample value of the input signal(y_(k-3), y_(k-2), y_(k-1), y_(k)) is (5.2, 5.2, 3.2, 1.2). E3 isobtained by E3=|Pa−Pb|−Pstd. E3 is 2.4. This means that the position ofthe mark start edge of the recording mark B1 is shifted rearward fromthe reference by 2.4.

In FIG. 20B, the position of the mark start edge of the recording markB1 is advanced to the ideal position. The sample value of the inputsignal (y_(k-3), y_(k-2), y_(k-1), y_(k)) is (4.8, 4.8, 2.8, 0.8). E4 isobtained by E4=|Pa−Pb|−Pstd. E4 is −2.4. This means that the position ofthe mark start edge of the recording mark B1 is shifted forward from thereference by 2.4.

Comparing the case of FIGS. 19A and 19B in which path A is the correctstate transition path and the case of FIGS. 20A and 20B in which path Bis the correct state transition path, the sign of the code representingthe shift direction is opposite. The sign of the code relies on therelationship between the expected value series of the correct statetransition path and the input signal series, and the relationshipbetween the expected value series of the other candidate path and theinput signal series. When the error between the input signal and theexpected value of the incorrect candidate path is large as in FIG. 19Band FIG. 20A, the value obtained by expression 11 has a positive sign.Namely, as the difference between the input signal and the expectedvalue of the incorrect candidate path becomes larger, the errorprobability of the maximum likelihood decoding is lower. In this case,the value obtained by expression 11 has a positive sign. The shiftdirection of the position of the mark start edge of the recording markcan be detected in consideration of this.

When path A is the correct state transition path in Pattern-1, Pattern-1is used for detecting the start edge of the recording mark of acombination of a 2T space and a 4T or longer mark. When path B is thecorrect state transition path in Pattern-1, Pattern-1 is used fordetecting the start edge of the recording mark of a combination of a 3Tspace and a 3T or longer mark.

Using the above-described method, an accumulation value or an averagevalue of each recording pattern (i.e., each mark length/space lengthcombination) is obtained, and a recording parameter is set such that theshift amount of the position of the start edge and termination edge isclose to 0. Thus, a recording control optimal for the maximum likelihooddecoding method is realized.

It is important to determine whether the start edge or termination edgeof a mark formed on a disc is located before or after the referenceposition. For the purpose of the determination, it is necessary todetect which pattern has a deviated edge. A shift amount is detected foreach pattern.

As described with reference to FIGS. 19A and 19B and FIGS. 20A and 20B,the sign of the code representing the shift direction is opposite.Therefore, for example, when a mark is shorter than a reference, themark has a minus sign. When the minus sign mark is longer than areference position, the mark has a plus sign. According to this rule,the above-described error value is analyzed for the start edge andtermination edge of each mark length, thereby making it possible todetect the length of the start edge and the termination edge of a marklength of interest. Therefore, the correction direction can bedetermined. In addition, the correction amount can be predicted based onthe absolute value of the detected value.

Optimization of a recording parameter will be described. The minimumpolarity inversion interval of a recording symbol is represented by m(in this example, m=2). The position of the start edge of a recordingmark formed on a recording medium may rely on the length of the spaceimmediately before the recording mark and the length of the recordingmark itself. For example, when the length of the space immediatelybefore the recording mark is mT to (m+b)T, the position of the markstart edge of the recording mark relies on the length of the spaceimmediately before the recording mark. When the length of the spaceimmediately before the recording mark is greater than (m+b)T, theposition of the mark start edge of the recording mark does not rely onthe length of the space immediately before the recording mark. When thelength of the recording mark itself is mT to (m+a)T, the position of themark start edge of the recording mark relies on the length of therecording mark itself. When the length of the recording mark itself isgreater than (m+a)T, the position of the mark start edge of therecording mark does not rely on the length of the recording mark itself.

The position of the termination edge of a recording mark formed on arecording medium may rely on the length of the space immediately afterthe recording mark and the length of the recording mark itself. Forexample, when the length of the recording mark itself is mT to (m+a)T,the position of the mark termination edge of the recording mark relieson the length of the recording mark itself. When the length of therecording mark itself is greater than (m+a)T, the position of the marktermination edge of the recording mark does not rely on the length ofthe recording mark itself. When the length of the space immediatelyafter the recording mark is mT to (m+b)T, the position of the marktermination edge of the recording mark relies on the length of the spaceimmediately after the recording mark. When the length of the spaceimmediately after the recording mark is greater than (m+b)T, theposition of the mark termination edge of the recording mark does notrely on the length of the space immediately after the recording mark. Inthe above, “a” and “b” are each an integer of 0 or greater, and theminimum polarity inversion interval of the recording symbol is greaterthan m+a and m+b.

In consideration of the position of the mark start edge and the positionof the mark termination edge of a recording mark, the optimization ofthe parameter Tsfp at the mark start edge needs to be performed on arecording mark adjacent to a space having a length of (m+b)T or less.The optimization of the parameter Telp at the mark termination edgeneeds to be performed on a recording mark having a length of (m+a)T orless.

FIG. 21 shows a list of recording parameters requiring optimization.Where, for simplicity, m=3 and a=b=3, the parameter needs to beoptimized for 32 recording patterns shown in FIG. 8. In FIG. 8, 2Ts2Tm,for example, means a pattern in which a 2T space exists immediatelybefore a 2T mark.

FIG. 22 shows a pattern(s) of the particular eight patterns which isused to detect a recording parameter requiring optimization. In otherwords, a pattern(s) of the above-described 8 patterns (Pattern-1 toPattern-8) which is used to detect each recording pattern (i.e., an edgepattern) is shown.

For example, the shift amount of the signal corresponding to a 2Ts3Tmrecording pattern (FIG. 22) is detected using P3A. P3A is Pattern-3 inwhich path A is the correct state transition path.

The shift amount of the signal of a 3Ts31Tm recording pattern (FIG. 21)is detected using P1B or P4A. P1B is a Pattern-1 in which path B is thecorrect state transition path. P4A is a Pattern-4 in which path A is thecorrect state transition path.

As can be appreciated from the above, a method for controlling arecording parameter optimal for the maximum likelihood decoding methodis to change the recording parameter such that the shift amount of thesignal corresponding to every recording pattern shown in FIG. 22 isclose to 0.

The shift amount of the signal corresponding to each of a 2Ts2Tmrecording pattern (a 2T space is present immediately before a 2T mark)and a 2Tm2Ts (a 2T space is present immediately after a 2T mark) cannotbe detected by any of the 8 patterns described above. Thus, the shiftamount needs to be optimized by another method (see FIG. 22). However,the 2Ts2Tm recording pattern and the 2Tm2Ts recording pattern have arelatively large value of reliability Pa−Pb and thus are not included inthe above 8 patterns. In other words, at the mark start edge or marktermination edge of the recording mark of each of the 2Ts2Tm recordingpattern and the 2Tm2Ts recording pattern, the error probability is low;it is not necessary to strictly optimize the recording parameter ofthese recording patterns. Therefore, an appropriate initial value may beused as the recording parameter instead of optimizing such shift amountsfor each information recording medium. Alternatively, the 2Ts2Tmrecording pattern and the 2Tm2Ts recording pattern may be optimized suchthat the accumulation value of the phase errors of the reproduced signalis minimal.

In the foregoing description, recording pulse (write strategy)adjustment is explained rather than power adjustment. The presentinvention is characterized in that a detection value (edge shift value),which is conventionally used for recording pulse adjustment, is used forpower adjustment. By using the above-described edge shift value, thelength of a recorded mark on a recording medium can be measured.Therefore, a recording power is adjusted so that a mark length becomes apredetermined length. A recording power parameter to be adjusted may beany of a write power, an erase power and a bottom power.

For example, a method for adjusting a write power parameter will bedescribed. While keeping a predetermined ratio relationship between anerase power and a bottom power, and a write power, test recording isperformed by changing a write power. A recording pattern is assumed tobe a 5T-single pattern. An edge shift value of 5Ts5Tm5Tm5Ts is detected(see FIG. 21).

FIG. 23 shows an edge shift value (filled triangle) of 5Ts5Tm, 5Tm5Tswith respect to a change in power, the absolute value (filled square) ofa 5T mark length measured based on an edge shift value (filled circle)of 5Ts5Tm, and an edge shift value of 5Tm5Ts.

The 5T mark length is obtained by addition of the edge shift value of5Ts5Tm and the edge shift value of 5Tm5Ts A recording power is adjustedso that the addition value becomes about 0.

Note that the above-described addition value and the target value of amark length may be change depending on the characteristics of a disc. Inaddition, a recording pattern may be a single pattern, a particularpattern, or a random pattern.

When a recording pattern other than a single mark is used, a width of amark is detected for each recorded mark length and power adjustment isperformed so that the average of all mark lengths or the sum of all marklengths is a target mark length for each disc.

Recording power adjustment may be performed for each of an environmentalchange (temperature, humidity), a change in characteristics in a diskplane, a required time, and a predetermined operation. In this case, arecording operation is suspended, an area recorded immediately beforethe suspension is reproduced, and a mark width is detected for eachrecorded mark length. When the mark length is determined to be short, arecording power may be increased depending on the mark width. When themark length is determined to be long, a recording power may be decreaseddepending on the mark width. The determination may be made based on allmark lengths. When only based on the width of a short mark having arelatively high sensitivity, it may be determined whether a power isincreased or decreased.

Mark lengths up to 5T have been described with reference to FIGS. 21 and22. For mark lengths of 5T or more, an edge shift value can be measuredfor each mark length.

Embodiments 1 to 3 of the present invention have been heretoforedescribed with reference to FIGS. 1 to 23.

The elements of the recording/reproduction apparatuses 100, 200 and 300of the present invention may be implemented as either hardware orsoftware. For example, an operation performed by at least one of theshaping section 8, the maximum likelihood decoding section 9, thereliability calculation section 10 and the recording medium controller11 may be implemented as a program which can be executed by a computer.

In Embodiments 1 to 3 of the present invention, the recording section103 and the recording section 303 record a piece of test informationonto the recording medium 1 using a plurality of recording powers.Alternatively, the recording section 103 and the recording section 303may record a plurality of pieces of test information onto the recordingmedium 1 using a plurality of recording powers. Further, the recordingsection 103 and the recording section 303 may record a piece of testinformation onto the recording medium 1 using a single recording power.Furthermore, the recording section 103 and the recording section 303 mayrecord a plurality of pieces of test information onto the recordingmedium 1 using a single recording power.

In Embodiments 1 to 3, an index M is defined by expression 6 includingthe variance of |Pa−Pb|−Pstd. The present invention is not limited tothis. For example, a value obtained by integrating Pa−Pb or |Pa−Pb|−Pstda predetermined number of times may be used as an index M.

In Embodiments 1 to 3, the recording pulse described with reference toFIG. 2 is used. The present invention is not limited to this. Forexample, the present invention can be applied to a recording powercontrol of a recording medium which does not require a cooling pulse(bottom power level). In this case, only a write power and an erasepower are controlled.

Further, in Embodiments 1 to 3, a test signal is not limited to thosedescribed above. A test pattern may be a combination of a relativelylong mark/space and a relatively short mark/space where the mark and thespace have the same probability of incidence. For example, such a testpattern includes a repeat pattern of 8Tm3Ts8Tm8Ts3Tm8Ts and a repeatpattern of 7Tm2Ts7Tm7Ts2Tm7Ts.

Further, in Embodiments 1 to 3, the recording modulation rule and thePRML technique are not limited to those described above. Variousrecording modulation rules and various characteristic PRML techniquesmay be combined. For example, (1, 7) Run Length Limited code and PR (1,2, 1) ML or PR (1, 2, 2, 2, 1) ML may be combined. 8-6 modulation code,which is used for CD and DVD, may be combined with the above-describedPRML technique.

Further, in Embodiments 1 to 3, power ranges which are searched for Pwo,Peo and Pbo are not limited to those described above. For example, eachpower search range may be ±x % (e.g., x=10) around a recommended value.If an optimum point is not detected in this range as shown in FIG. 18,an upper or lower limit may be provided.

Further, in Embodiments 1 to 3, when Pwo is searched for, the parameteris changed while the Pe/Pw ratio is fixed. The present invention is notlimited to this. For example, Pwo may be obtained by changing Pw whilePe and Pb are fixed to appropriate values.

The optical disc recording/reproduction apparatus of the presentinvention optimizes a recording power during recording by using areproduced signal evaluation index which is correlated with decodingperformance in a processing system employing maximum likelihood decodingfor processing a reproduced signal. As a result, a recorded state can beoptimized and errors can be minimized during reproduction. In thepresent invention, a change in reproduced waveform due to a change inrecording power can be detected with high precision, as compared to whena reproduced signal quality index, such as jitter, asymmetry, BER or thelike, which are conventionally used for recording power control is used.Therefore, recording power control can be performed with high precision.Since a recording power can be determined with high precision,performance degradation due to cross power can be minimized, resultingin stable compatibility of optical disc drive apparatuses and opticaldisc media having the same standard.

Conventionally, no appropriate parameter can be obtained with highprecision using a reproduced signal evaluation index, such as jitter,asymmetry, BER or the like to determine and set an optimum recordingparameter with high precision.

In the present invention, by detecting a state, which is recorded usinga metric expected value error of only a state transition pattern (apattern with the minimum Euclid distance) involved in the vicinity of anedge of a reproduced waveform among a number of state transitionpatterns in the PRML algorithm, variations in the power of a recordingleading pulse (write power), the bottom power of a cooling pulse or theratio of a write power/an erase power can be detected with highprecision, and based on the result, a recording power is controlledduring recording to optimize a recorded state. In order to performrecording power control with higher precision, a test signal for use intest recording has a particular pattern capable of detecting a change ina reproduced waveform corresponding to a change in a recording powerwith high precision.

Although certain preferred embodiments have been described herein, it isnot intended that such embodiments be construed as limitations on thescope of the invention except as set forth in the appended claims.Various other modifications and equivalents will be apparent to and canbe readily made by those skilled in the art, after reading thedescription herein, without departing from the scope and spirit of thisinvention. All patents, published patent applications and publicationscited herein are incorporated by reference as if set forth fully herein.

1. A recording/reproduction apparatus, comprising: a first recordingsection for recording at least one piece of test information onto amedium using at least one recording power; a reproduction section forreproducing at least one test signal indicating the at least one pieceof test information from the medium; and a second recording section forrecording information onto the medium using one of the at least onerecording power, wherein the reproduction section comprises: a decodingsection for performing maximum likelihood decoding of the at least onetest signal and generating at least one binary signal indicating aresult of the maximum likelihood decoding; a calculation section forcalculating a reliability of the result of the maximum likelihooddecoding based on a test signal of the at least one test signalcorresponding to an edge of a recorded mark formed on the medium and abinary signal of the at least one binary signal corresponding to theedge of the recorded mark; and an adjustment section for adjusting arecording power for recording the information onto the medium to the onerecording power based on the reliability.
 2. A recording/reproductionmethod, comprising: recording at least one piece of test informationonto a medium using at least one recording power; reproducing at leastone test signal indicating the at least one piece of test informationfrom the medium; and recording information onto the medium using one ofthe at least one recording power, wherein the reproducing stepcomprises: performing maximum likelihood decoding of the at least onetest signal and generating at least one binary signal indicating aresult of the maximum likelihood decoding; calculating a reliability ofthe result of the maximum likelihood decoding based on a test signal ofthe at least one test signal corresponding to an edge of a recorded markformed on the medium and a binary signal of the at least one binarysignal corresponding to the edge of the recorded mark; and adjusting arecording power for recording the information onto the medium to the onerecording power based on the reliability.